MCRH question

[braddsn]

Hey fellas... quick question about MCRH, more of an advanced question for more advanced builders. A fellow builder (XP) and I were recently discussing ratios of bp on rice hulls. After a lot of conversing, and watching some of Ned's burst videos over and over, we both ended up with the same question...which is: What kind of difference does it make going from say 4:1, to 5:1, 6:1, 7:1, etc. I have always made mine 7:1. From the videos I have seen, and from discussions I have had with guys, the ratio doesn't seem to make a difference, which to me means the following: It is going to take (x) amount of energy to accomplish a certain task (in this case, break a shell nice and big). With that being said, the guy with the 4:1 ratio and the guy with the 7:1 ratio will be essentially adding the same amount of bp into the shell, but with different amounts of rice hulls. Is this the case? The reason I ask is.... I make a couple hundred kilo's of MCRH per year for both lifting and breaking. IF changing the ratio could somehow be more efficient and use less bp, that sounds very attractive. But my physics-based mind is telling me that (X) amount of energy is needed, regardless of ratios. Ok, ramble over.

[Mumbles]

The first thing to do would probably be to measure bulk density. This would give you a better idea of what amount of BP you're really adding to a given shell, and may give better insight into how the ratio really effects break performance. I would expect that higher BP to rice hull ratios truly do add more BP. BP is significantly more dense than rice hulls. Essentially you have 2 extremes; 100% rice hulls (~1lb per gallon or .12g per mL), and 100% granulated BP. I don't off hand recall the bulk density of BP, but I think pressed and corned material is around 8lbs per gallon or 1g per mL. That could be way off. I'd be happy to be hear some real measured values. I'd suspect screen granulated is maybe 20% less dense than that.

 

The real answer to this question is kind of muddied by the heavy booster usage some people utilize. The true effect of the coating ratio, quality of BP, etc. can be covered up by a booster adjustment.

[AzoMittle]

I can't provide all the numbers (lack of time for note taking) but I can provide some anecdotal input.

 

I'd like to say up front the size of the shell does seem to have a significant impact; I was making 6" plastic, the guys making 3" plastic had to use almost the same amount of booster to get a symmetrical break.

 

Last event I ended up using all of my coated rice hulls in the first day or so; those were coated 5:1 by a professional vendor, and required around 2 scoops of booster* from a normal plastic spoon to get a good break. After running out I made some more myself, I was running low on BP but had plenty of rice hulls, so, I coated a batch at about 3:1 and then mixed that half and half with completely uncoated hulls to bulk it up.

 

I ended up using about 1 (maybe 2) extra scoops of booster but a whole lot less BP. All stars lit in both methods and it was impossible (for me) to tell the difference in bursts. I also use quite a bit more lift than an ounce per pound, so my 6" lift like 8"+, but I doubt the extra height really makes a difference for the matter at hand.

 

 

*edit: I forgot a word.

Edited April 15, 2016 by AzoMittle

[braddsn]

Thanks guys for the responses. And I agree about the booster. You factor booster in and it changes everything. I am going to drop down to 5:1 from 7:1 and just see what happens.

[BlueComet24]

Mumbles, my -16 mesh riced BP is about 1.3g/cm³. I believe corned BP is commonly pressed to 1.7g/cm³ before being broken up.

 

I'd suspect that there are diminishing returns when coating more BP onto rice hulls, because with a very thick layer, the stuff in the middle might not burn before the shell is broken, thus not aiding in breaking the shell much.

[AzoMittle]

It seems your goal is to get the coating ratio as low as possible in order to save on costs. I ran some numbers to do a price comparison, results first, then method so you can tune it.

 

Results:

 

Ratio Price/Lb Change in Price

1:01	2.0875	      0.495833333
2:01	2.583333333   0.247916667
3:01	2.83125	      0.14875
4:01	2.98	      0.0991666667
5:01	3.079166667   0.0708333333
6:01	3.15	      0.053125
7:01	3.203125      0.04131944
8:01	3.24444444    0.03305556
9:01	3.2775	      0.0270454545
10:01	3.304545455	

*Note: Can someone please confirm if I got my math right? It feels odd that 5:1 and 10:1 are such a minor difference instead of almost double....

 

 

Method:

 

Final Price per Pound = (Coating Ratio * BP Price / (1 + Coating Ratio)) + RH Price

 

Price per Pound for Composition = ((Ingredient 1 * Amount 1) + (Ingredient 2 * Amount 2) + .... (Ingredient N * Amount N)) / 100

 

For example, my costs would be:

• Rice Hulls: $0.60 / Lb
• KN: $3.00 / Lb
• Sulfur: $2.50 / Lb
• Charcoal: $3.00 / Lb

Price per Pound for BP: ((3 * 75) + (3 * 15) + (2.5 * 10)) / 100 = $2.975

 

Final Price: (5 * $2.975 / (1 + 5)) + $0.60 = $3.079166667

 

I use an excel sheet to do this automatically for all of my formulas to figure out how much it will cost me. It works great when you have multiple formulas to pick from that will all work, you can simply choose the cheapest. For example, the typical 75:15:10 costs me $2.975 while Shimizu's Burst Charge #44 (70 KN : 30 Charcoal + 2% SGRS) costs me $3.02. Similarly, a standard 70 KP : 30 Al booster costs me $8.75 per pound while a K Benz / CuOxy whistle booster costs $6.92 per pound.

 

If anyone is able to get some measurements on how much (by weight) coated rice hulls (and at what ratio) and booster they use in their shells I can do some price comparing magic to find the cheapest combo's of burst charge and booster. Once you start using booster you can lower the coating ratio (IMHO), how much will depend on what type of booster, what type of burst charge, your coating ratio, and the shell size and type. Finding the cheapest burst charge or the cheapest booster is simple, finding the cheapest combination won't be but it is definitely possible.

Edited April 15, 2016 by AzoMittle

[BlueComet24]

Not sure how you got $2.975/lb for BP, AzoMittle. Eh, close enough.

.75*3+.15*3+.1*2.5=$2.95/lb

 

The equation would be (.6+2.95x)/(x+1) where x is the number of parts of BP coated to the hulls. The limit as x->∞ is 2.95, which makes sense because infinite parts of BP with a negligible 1 part rice hulls would approach the cost of pure BP. Anyway, here are the numbers I got:

Ratio $/lb Change

1:0    0.600    N/A
1:1    1.775    1.175
1:2    2.167    0.392
1:3    2.363    0.196
1:4    2.480    0.118
1:5    2.558    0.078
1:6    2.614    0.056
1:7    2.656    0.042
1:8    2.689    0.033
1:9    2.715    0.026
1:10   2.736    0.021

My equation for the difference is the current cost minus the previous cost.

Edited April 15, 2016 by BlueComet24

[schroedinger]

Why so complicated?

Price per kg:

 

(Parts of bp × price of bp per kg + parts of ricehulls × price of ricehukls per kg) / (parts of bp + parts of ricehulls)

 

For you at 7:1

 

(7×2.975 + 1×1.20) / (8+1) = 5.3125

 

This also allows for use of lb, ounce, tonns whatever if you just modify the price to per ....

Your calculating is wrong at the + price of RH part. You adjust the price of bp to 1 pound of product and add to this 1 pound of rice hulls ( or in other words your equation calculates what the bp in a x:1 ratio costs per pound and then coats this ammount onto 1 pound of RH). At a 7:1 ratio you make 0.875 pound of RH cost 2.60 and 1 pound of RH is 0.60 = 3.20. But thats the actual price for 1.875 pound in a 0.875 : 1 ratio.

Edited April 15, 2016 by schroedinger

[Peret]

I've always used 4:1 for my breaks, sometimes with a gram of flash booster for 3 inch, and I get quite acceptable breaks. The secret to getting the best out of the burst is getting the pasting strong and uniform. Without good confinement any amount of BP is useless.

[braddsn]

Azomittle, actually, my goal was not to reduce cost. For me, the cost of bp per kg is so small that I don't really consider it much. It's more about the work and time involved. Cooking the charcoal, processing it, milling the bp, emptying the mill jar, etc. I know it sounds lazy, I am not lazy... I am just trying to streamline as much as possible because I build a lot of shells (upwards of 500 per year.. mostly 4's 5's, and 6's). And, what interests me even more is... at what ratio does your return start to diminish. It seems like most information I am finding is saying that there really is not a difference in performance between say 5:1 and 7:1. Hopefully I am making sense.